A coffee grinder is a device for grinding coffee beans, for example, for brewing coffee. A coffee grinder comprises a grinding tool for grinding coffee beans and a motor for driving the grinding tool. A coffee grinder can be a stand-alone device or integrated, for example, in a fully-automated coffee machine as commercially available by the applicant.
U.S. Pat. No. 7,984,868 discloses a coffee grinder with two grinding burrs. One of the grinding burrs is driven by a motor, whereas the other burr is static. The two grinding burrs are provided with grinding surfaces against which coffee beans are ground. The grinding surfaces are spaced a desired dimension away from each other to produce a desired grind of coffee. A closer separation of the grinding surfaces results in finer coffee whereas a larger separation results in coarser coffee grind. Adjustment means are provided for automatically adjusting the separation of the burrs relative to each other.
A possible failure condition occurs if the coffee grinder is blocked by jammed beans, bean particles or coarse grind. The coffee grinder stalls. Such a stall condition can be detected as described in EP 2 030 539 A1 which discloses a method for counting the number of revolutions of a burr of a coffee mill. EP 2 030 539 A1 teaches to consequently shut of the motor before it is damaged but does not provide a solution to overcome the stall condition.
As a solution EP 0 616 502 B1 suggests the use of a grinder motor of sufficient grinding power to overcome this problem by brute force. A disadvantage of this solution is that a powerful motor is heavy, bulky and/or expensive.
As an alternative solution, the operating manual of the WMF5 coffee grinder teaches to manually adjust the grinding degree to a coarser setting, i.e., to increase the separation of the grinding surfaces. Thereby, the jammed beans are released. After increasing the separation, the user has to clear the grinder, manually readjust the desired grinding degree and can then resume grinding operation. A disadvantage of this solution is that it requires manually adjusting the separation of the burrs and clearing the coffee grinder which is a tedious and time-consuming process.
GB 488 084 A discloses that an electric motor driving a coffee grinder has its rotor mounted freely on its shaft to which it is connected by a spring which tends to move the rotor relative to the shaft into an initial position beyond which it is prevented from moving. The movement of the rotor with respect to the shaft in the reverse direction is also limited so that on starting the rotor takes up the shaft with an impact, and on stopping the rotor is moved back on the shaft by the spring and gives the shaft an impact in reverse direction. GB 488 084 A teaches to clear the coffee grinder after the grinding process as a preventive measure to facilitate re-starting.
EP 1 707 089 A1 discloses a method for detecting a lack of coffee beans in a coffee grinder by evaluating a level and/or spectrum of vibrations caused by the coffee grinder during operation.
FR 1 215 254 A discloses an automatic control for home appliances such as coffee grinders to provide automatic shutdown.
EP 2 153 758 A1 discloses a method for determining the load of a mill, wherein the state of the mill is derived from the revolution speed of the mill. The revolution speed can be measured e.g. using a Hall sensor. If the mill is blocked the motor driving the mill can be stopped the user can be requested to remove the blockage.
GB 2 463 900 A discloses a coffee dispensing apparatus having a grinding mechanism. In the event that the grinder becomes jammed during a grinding operation, a drive dog of the grinder will stop rotating. The motor driving the grinder will be decoupled from the grinder by a clutch. The motor is then stopped and an alert may be generated to advise the user that the grinder has become jammed.